1. Field of the Invention
The present invention generally relates to methods for forming silicon oxide films on substrates via atomic layer deposition (hereinafter, referred to as ‘ALD’) processes, and more specifically, to a method for forming a silicon oxide film at low temperature and high deposition rate using Si2Cl6 (hexachloro disilane; hereinafter, referred to as ‘HCD’) and H2O sources, and catalysts.
2. Description of the Prior Art
Generally, a silicon oxide film is one of the most commonly used thin films in a semiconductor since it provides superior interface with silicon and has excellent dielectric characteristics. There are two conventional methods for depositing a silicon oxide film: (1) oxidation process wherein silicon is oxidized at a temperature of more than 1000° C.; and (2) a Chemical Vapor Deposition (CVD) process wherein more than two sources are provided at a temperature ranging from 600 to 800° C. These methods cause diffusion on interface due to high deposition temperature, thereby degrading electrical characteristics of devices.
As semiconductor devices having memory capacity of more than giga bytes are currently required to be manufactured, thin films used in semiconductor devices should be controlled at the atomic layer level. Further, the thin films are required to have excellent step coverage and low deposition temperature to prevent diffusion and oxidation at the interfaces. To satisfy the requirements, an atomic layer deposition process has been proposed.
Conventionally, the silicon oxide film is deposited at a temperature of more than 600K via the atomic layer deposition process using SiCl4 and H2O sources. The conventional deposition process is as follows.
First, a SiCl4 source is provided in a reaction chamber containing a substrate having hydroxyl group (—OH)s on its surface. The SiCl4 source reacts with the hydroxyl group, and —SiCl3 is adsorbed on the surface of the substrate, HCl by-products are formed (see Reaction Formula 1). When the reaction of SiCl4 with the hydroxyl group is saturated, the remaining SiCl4 no longer reacts (self-limiting condition), and the surface of the substrate has —SiCl3 surface chemical species adsorbed thereon.—OH*+SiCl4→—O—Si—Cl*3+HCl  [Reaction Formula 1]
When the above reaction is complete, the H2O source is provided to the reactor chamber. The H2O source reacts with the —SiCl3 surface chemical species to generate adsorption of the hydroxyl group thereto and HCl by-products (see Reaction Formula 2). When the reaction of H2O with the —SiCl3 surface chemical species is saturated, the remaining H2O no longer reacts (self-limiting condition), and the surface of the substrate has hydroxyl groups adsorbed thereon.—O—Si—Cl*+H2O→—O—Si—OH*+HCl  [Reaction Formula 2]
The above-described process is repeated to deposit the silicon oxide film. However, the conventional method requires high temperature of more than 600K, long time necessary for deposition and a large amount of sources.
In order to solve the foregoing problems, a method for forming silicon oxide films at a temperature below 200° C. using catalysts and small amount of sources is disclosed in U.S. Pat. No. 6,090,442. The disclosed method uses catalysts, which allows silicon oxide to be deposited even at a temperature below 200° C. However, the disclosed method has the following problems.
First, when a silicon oxide film is deposited at a temperature ranging from room temperature to 50° C., the by-products from the reaction and unreacted liquid sources such as HCD and H2O are not easily removed due to low temperature in the reactor chamber. These materials exist as particles in the thin film after deposition, which deteriorate properties of the thin film.
Second, when a silicon oxide film is deposited at a temperature above 50° C., by-products resulting from reaction and unreacted liquid sources such as HCD and H2O are easily removed. However, the deposition rate of thin film is very low. That is, when a silicon oxide film is deposited using SiCl4, H2O and catalysts at a temperature above 50° C., the deposition rate is lower than 1.0 Å per cycle (see FIG. 1). As a result, the yield of device is reduced.
When a silicon oxide film is deposited via the above conventional atomic layer deposition process, residuals are generated in a reactor chamber during the formation process by a plurality of reaction gases. These residuals are adsorbed to a heater, a disc, and an outside wall and an upper surface of reactor chamber as well as the substrate. The residuals in the atomic layer deposition reactor are removed by in-situ cleaning which uses thermal or plasma method using NF3 gas. The cleaning method is used in deposition process of silicon oxide film performed at temperature above 400° C.
As a result, when a silicon oxide film is deposited via the atomic layer deposition process at low temperature below 400° C., in-situ cleaning cannot be performed.